The development and design of radio receivers, transmitter, and/or transceiver systems has been driven by the great demand for devices for mobile wireless communication applications, especially handset devices. With the ever decreasing size of mobile handsets and an ever increasing demand for voice, data, and/or video processing capabilities, there is an growing need to develop radio receivers and transmitters that not only meet these challenging performance requirements, but that do so in smaller integrated circuit (IC) footprints, that is, at lower cost, and with greater power efficiency. One approach that aims at addressing these demands is the development of highly integrated receivers, transmitters, and/or transceivers in complementary metal oxide semiconductor (CMOS) technology to minimize the number of off-chip components.
As a result of these highly integrated systems, radio receivers, transmitters, and/or transceivers may comprise a large number of components and/or circuits, which may be utilized for the processing of signals. The design of optimal systems may require that these components and/or circuits operate within certain requirements or constraints for a wide range of operational conditions. For example, power amplifiers (PA) and/or low noise amplifiers (LNA) may be required to operate at an optimal gain level. However, this gain level may vary significantly based on operational conditions, such as temperature and/or voltage supplies, or based on manufacturing conditions, such as the non-uniformity in transistor parameters that result from normal variations in the manufacturing process. These variations generally referred to as process, voltage, and temperature (PVT) variations, may have a significant effect in the overall performance of wireless handsets.
In systems based on the global system for mobile communications (GSM) standard, for example, PVT variations in many of the circuits and/or components utilized in the receiver or the transmitter may produce errors in the generation of “I” (in-phase) and “Q” (quadrature) signal components. These errors may result in a significant degradation in the signal-to-noise ratio (SNR) and/or the bit-error-rate (BER) performance of GSM handsets.
In-phase (I) and quadrature (Q) signals are typically utilized in modulation and demodulation sections of transceivers in cellular handsets and other types of communication devices. The I and Q signals, which are 90 degrees out of phase, may be generated, for example, by coupling an input local oscillator signal to first and second outputs via different RC networks. For example, one RC network may include a capacitor coupled between the input and the first output and a resistor coupled between the first output and ground and the other RC network may include a capacitor coupled between the input and the second output and a resistor coupled between the second output and ground. To achieve balanced I and Q signals or I and Q signals having the same amplitude, the resistors in each RC network and the capacitors in each RC network must have the same and predetermined value according to the operation frequency. However, process variations, particularly in the resistors, can cause the I and Q signals to significantly differ in amplitude, thereby undesirably affecting transceiver performance.
In one approach, system level calibration can be used to reduce the difference in amplitude between the I and Q signals. However, system level calibration may not be effective in instances where the difference in amplitude of the I and Q signals is too great. In another approach, calibrated resistors may be utilized in the RC networks to achieve I and Q signals having similar amplitudes. However, at high local oscillator frequencies, such as 5.0 GHz, each RC network requires a very small value resistor, which is difficult to calibrate.
Further limitations and disadvantages of conventional and traditional approaches will become apparent to one of skill in the art, through comparison of such systems with some aspects of the present invention as set forth in the remainder of the present application with reference to the drawings.